You may simply have a kink in the inner tube. Deflate the tube, pry one side of the tire out of the rim, pump the tube up slightly and examine all the way around to make sure it is evenly placed around the rim, then deflate it and remount that side of the tire.
Also when you finally start to reinflate it, push the stem a bit into the rim to make sure that the reinforced area of the tube around the stem is inside the tire bead and not trapped under it